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Research found that Eastern Canada has a much greater issue with soil-borne diseases than previously thought. The primary culprit is the potato early dying complex. (Photo: Bernie Zebarth, AAFC)

Solving Eastern Canada’s Yield Woes

Researchers strive to jump-start Maritime Canada’s sluggish yield gains.

As a large-scale soil rejuvenation study in New Brunswick draws to a close, lead researcher and Agriculture and Agri-Food Canada potato scientist Bernie Zebarth says solutions to lagging potato yield in Eastern Canada are anything but simple.

For decades, potatoes have held top position as Maritime Canada’s most important cash crop. In 2015-2016, New Brunswick, Prince Edward Island and Nova Scotia produced 1.84 million tonnes of potatoes for a value of $256 million in total farm receipts. Yet, the region’s yield is falling behind other key production areas: whereas Alberta and Manitoba increased average yields by four hundredweight (cwt) per acre per year since the late 1980s and American farmers are ratcheting up even higher gains, New Brunswick only achieved a 1.4 cwt/acre per year gain during the same period.

“Global competition is the real driver of research because we have to maintain competitiveness. As input costs continue to go up, we need to have a similar increase in productivity,” says Zebarth. “The primary market for potatoes coming out of P.E.I. and New Brunswick is the eastern seaboard. If our cost of production gets too high, they’ll just bring in fries and other product from the western U.S. Right now, our dollar is low so our potato exports are competitive, otherwise we’d have a real problem.”

In January of 2013, industry approached Agriculture and Agri-Food Canada (AAFC) researchers in hopes they might discover the cause of the lag and find workable solutions.

The team tried multiple strategies to overcome yield limitations; jumping in, Zebarth says, before they had complete insight into the problems.

Some of their initial strategies offered limited success in the short term, though Zebarth notes they may yet pay off in the longer term.

Employing tillage options that promote surface residue, thereby decreasing winter erosion, might slow soil losses but did not promote much immediate yield gain. Growing barley as a nurse crop to four inches, then burning it off with herbicide and incorporating the additional organic matter as part of the hilling process reduced soil erosion and loosened compaction, but yield increases were modest and somewhat inconsistent. And planting fall cover crops was even less successful; since fall in the Maritimes is typically quite cool post-potato harvest, cover crops did not grow enough to offer measurable benefits.

As the research progressed, the team determined the two most limiting production factors in Maritime fields are soil-borne disease and declining soil health.

Soil-borne disease comes primarily in the form of potato early dying complex: a combination of Verticillium wilt and parasitic nematodes, particularly root lesion nematodes common in Eastern Canada.

“We knew there were soil-borne diseases but we didn’t know how important they are in limiting yield,” says Zebarth. “The complex is synergistic. If you have both Verticillium wilt and parasitic nematodes, they build on each other: A plus B equals a C that is bigger than just the sum of A and B.”

Once the team realized the impact of soil-borne disease, it shifted its focus for ongoing research to include heavier investment in seeking solutions to potato early dying complex. Beginning in 2017 and looking forward, the research team is developing new tools to measure pathogen levels, working to improve understanding of the specific pathogens present in potato growing regions, evaluating newly registered pest control products for control of Verticillium wilt and parasitic nematodes, and evaluating novel cropping systems to reduce pathogen levels.

The current approved project ends next month, in March 2018. Zebarth says the team is submitting an industry-led Canada-wide funding proposal to continue the work on potato early dying over the next five years. If successful, the work would be led by Dr. Mario Tenuta from the University of Manitoba and carried out in New Brunswick, P.E.I., Ontario, Quebec, Manitoba and Alberta.

Focus on Soil Health

Alongside seeking answers on the soil-borne disease front, the researchers simultaneously dug into soil health concerns. Eastern Canada’s wetter climate and steeper sloped land means Maritime potato fields are vulnerable to erosion, drainage issues and compaction. Even more challenging, the thin, low organic-matter soils leave far less buffer than deeper, healthier soils found in Manitoba and Alberta.

Zebarth wondered if augmenting the soils with compost to increase organic matter, loosen compaction and enhance water holding capacity might be the answer. In 2014, he began a four-year, multi-pronged compost study in collaboration with Potatoes New Brunswick, the PEI Potato Board, McCain Foods Canada and the Manitoba Horticulture Productivity Enhancement Centre (MHPEC).

The compost study consisted of field-scale compost application overseen by McCain Foods Canada, and a small plot experiment managed by AAFC researchers at the Fredericton Research and Development Centre.

At the field scale trials, 45 metric tonnes per hectare of a wood shaving and poultry litter compost were incorporated into the same fields in each of three consecutive years. Each year the fields were cropped to potatoes, the soil was tested for key soil health indicators, and potato yield and quality were analyzed.

While anyone who grows crops innately understands compost is positive for crops, the reality is that scientists do not yet know how various compost products and differing compost production processes individually impact potato growth. As such, Zebarth opted to also include a small-plot trial to analyze the soil’s response and crop’s productivity to a variety of other compost options. The plot trials included a forestry residue compost, an organics compost, a poultry manure + bark compost, and a marine-based compost, each applied at about twice the rate of the field-scale study.

The results from both the field-scale and small plot compost studies are a “mixed success,” says Zebarth.

While the field scale trials mostly achieved modest yield benefit, the small plot trials showed little immediate production benefit.

“The good news is yes, we can in a short time period greatly improve some aspects of soil heath. But we cannot improve all aspects; and those that we can improve are not necessarily going to increase yield every year.”

To the researchers’ surprise, adding compost did not increase the soil’s water holding capacity by much; neither did it increase biological activity.

“We got the benefit that soil is not as dense and compact, but because the carbon we had left in compost was not biologically active, we didn’t seem to get the biological benefit we expected.”

Equally surprisingly, all five of the compost options gave a relatively similar crop yield and soil health response.

“No single compost proved a clear winner. The biggest difference varied in terms of the amount of ash in the compost: the more ash you have, the less organic matter. Any response we saw was based on the quantity of organic matter.”

While results were not the huge and obvious gains farmers would prefer, Zebarth cautions that longer-term benefits may not yet be obvious.

“This study was only conducted over four years. One possibility is that composts based on wood waste may require longer before we see the benefits. Compost is not a quick fix, you can’t necessarily expect immediate results.”

The results are not conclusive enough for Zebarth to recommend Maritime growers begin large-scale application of compost. That said, the challenges facing eastern Canadian potato fields are varied and often complex. While compost will not solve all issues, it may offer direct benefit in certain situations. Heavily compacted soils, for example, will benefit from the loosening effect of compost application. And all soils will benefit from farmers who consistently work to build up rather than mine them.

Zebarth says knowing when to use compost, like knowing how to get the best benefit from any input, will depend more and more on knowing your fields’ variability. Analyzing crop productivity and soil health by area and then targeting treatment not only makes the cost of an input like compost more modest, it will offer more obvious results.

“Analyzing variability is already happening in other parts of the world but we’re lagging behind, at least in New Brunswick which is the area I know best. My impression is that growers in the west are further ahead than growers here (in the Maritimes).”

Zebarth has high hopes for Maritime Canada’s potato growing future. He says many farmers are now asking good questions, testing out new practices and being more open to the concept of variable application. He hopes the subtle shift is just the start of big changes ahead, driven by farmers and supported by researchers and industry.

“It really has to come from growers. Growers have recently come to the realization that it’s time to increase our gain. We have to look at all the options for what we can do to increase yield, but it has to be growers pushing it forward, because they are the true innovators finding out what works on their farms,” he says.

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